Building a Federated Image Exchange: My Summer Vacation

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The Inland Northwest, which we call home, is fortunate to have a legacy of health-information sharing among many organizations. These include the 97-radiologist private practice Integra Imaging (Spokane, Washington), formed through the merger of Inland Imaging and Seattle Radiology. Integra Imaging’s PACS archives host images for more than 100 sites. As more organizations in the greater region want to move images beyond regional borders, we are faced with an increasing need to share images across disparate PACS to meet the needs of the health-care organizations we are affiliated with—in the Pacific Northwest and beyond. We hear a lot about image exchanges hosted in clouds and about making it possible to share images with anyone, anywhere. Such exchanges, however, come with a cost. For sharing images with organizations on a routine basis, the cost per transaction of sharing 7,500 images (the number of CDs that we burn per year) exceeds the cost of burning the CDs. While this calculation doesn’t account for efficiency gained, it’s a clear signal that alternative approaches should be considered. The 2011 publication of supplement 148 by the DICOM Standards Committee1 opened the door to using Web services to share images over the Internet in a manner that’s much simpler than the HTTP approach that was specified originally. This inspired us to look at building an alternative to cloud-based exchanges by using federated sharing, directly, among participants. To see whether this approach was technically feasible, we endeavored to build a proof-of-concept project using standards, technical specifications, and frameworks from Integrating the Healthcare Enterprise® (IHE), NEMA, and the RSNA to demonstrate the exchange of images among federated PACS using standards-based Internet transactions. Just the Specs, Please While there are many different standards that could be used to share images, IHE has published a set of technical specifications as the Cross-enterprise Document Sharing for Imaging (XDS-I.b) integration profile² to facilitate the development of systems that can publish, find, and retrieve images, across enterprises, over the Internet. In essence, this profile describes a federated approach to image storage that uses a patient-identity manager and record-locator service. Each participating site is responsible for the local storage of its images and for registering them with the central registry. Only basic patient demographics and image lists (but no actual images) are stored in the central registry. Each site is able to query the central registry for a list of images available at foreign sites. Data from this list enable a site to download the appropriate images from the foreign sites directly. This federated architecture allows an installation to connect to a virtual cloud while using its existing PACS infrastructure. The XDS-I.b profile, however, is currently in the trial-implementation phase. During this phase, certain components might be speculative and subject to revision/modification. Health IT vendors are presented with the opportunity to implement and test the profile at this time. To explore options on behalf of Integra Imaging, we developed and implemented a working PACS–XDS-I.b proxy agent that, together with separate IHE registry/repository software, fulfills the requirements of the XDS.I-b profile. We call this proxy the Edge Gateway. Because it was written in Java, the Edge Gateway could theoretically run on any major operating system, on any basic computer or server. The Edge Gateway runs on RSNA code, which (in turn) uses OpenHealthTools and Apache Axis. It also makes use of dcm4che code for DICOM–related tasks. All of the code is based on free and open-source software. A primary function of the IHE registry is to reconcile different facilities’ medical-record numbers to a single master patient index. The Edge Gateway acts as a broker for the publishing, finding, and retrieving of images. The registration process begins when image acquisition occurs. The site’s PACS then notifies the Edge Gateway, which provides an image manifest to the IHE repository and registers it with the IHE registry. The image manifest is now available to trusted foreign sites for perusal. The Edge Gateway also provides a site with the ability to find images that are available from other sites. Search functionality is initiated when a patient is registered with the site’s health-care information system, which then notifies